Effects of rapeseed oil on the rhizodegradation of polyaromatic hydrocarbons in contaminated soil.

Plants have the ability to promote degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soil by supporting PAH degrading microorganisms in the rhizosphere (rhizodegradation). The aim of this study was to evaluate if rapeseed oil increases rhizodegradation because various studies have shown that vegetable oils are able to act as extractants for PAHs in contaminated soils and therefore might increase bioavailability of PAHs for microbial degradation. In this study different leguminous and grass species were tested. The results suggested a significant impact of vegetable oil (1 and 3% w/w) on plant growth (decrease of plant height and biomass). The results of the pot experiment showed a decrease in the PAH content of the soil without amendment of rapeseed oil after six months. In soil amended with 1% and 3% of oil, there was no decrease in PAH content within this period. Although no enhancement of PAH degradation by plants could be measured in the bulk soil of the pot experiments, a rhizobox experiment showed a significant reduction of PAH content in the rhizosphere of alfalfa (Medicago sativa cv. Europe). Our investigations also showed significant differences in the degradation behaviour of the 16 individually analysed PAHs.

Carbonaceous soil amendments to biofortify crop plants with zinc.

Carbonaceous soil amendments, comprising mixtures of biosolids and biochar, have been demonstrated to improve fertility while reducing nitrate leaching. We aimed to determine the efficacy of a biosolids/biochar soil amendment in biofortification of vegetables with Zn, an element that is deficient in one third of humanity. We grew beetroot (Beta vulgaris), spinach (Spinacia oleracea), radish (Raphanus sativus), broccoli (Brassica oleracea), carrot (Daucus carota), leek (Allium ampeloprsum), onion (Allium cepa), lettuce (Lactuca sativa), corn (Zea mays), tomato (Solanum lycopersicum), and courgette (also called zucchini - Cucurbita pepo) in an unamended soil (silt loam, pH 5.6), and soil amended (by volume) with 10% biosolids, 20% biochar, and 10% biosolids+20% biochar. The biosolids and biosolids+biochar treatments significantly increased the biomass and Zn concentration of most species, with a large interspecific variation. Beetroot showed the greatest increase, with dry weight Zn concentrations of up to 178 and 1200 mg kg(-1) in the bulbs and leaves respectively. Cadmium, Cu and Pb were below guideline levels in all samples, except the leaves of spinach and beetroot, which slightly exceeded the World Health Organisation's maximum permitted concentration of 0.1 mg Cd kg(-1) fresh weight. A mixture of biosolids and biochar is an effective means to biofortify crops with edible leaves as well as beetroot with Zn. Future research should investigate the efficacy of the system in other soil types and the role of biochar in the immobilisation/inactivation of organic contaminants and pathogens contained within the biosolids.